netdev - Re: [PATCH 1/2] net: Toeplitz library functions

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Message-Id: <20130924.144906.781831317299527167.davem@redhat.com>
Date:	Tue, 24 Sep 2013 14:49:06 -0400 (EDT)
From:	David Miller <davem@...hat.com>
To:	bhutchings@...arflare.com
Cc:	therbert@...gle.com, David.Laight@...lab.com,
	netdev@...r.kernel.org, jesse.brandeburg@...el.com
Subject: Re: [PATCH 1/2] net: Toeplitz library functions

From: Ben Hutchings <bhutchings@...arflare.com>
Date: Tue, 24 Sep 2013 19:10:45 +0100

> On Tue, 2013-09-24 at 14:03 -0400, David Miller wrote:
>> From: Tom Herbert <therbert@...gle.com>
>> Date: Tue, 24 Sep 2013 08:54:24 -0700
>> 
>> > On Tue, Sep 24, 2013 at 8:39 AM, David Miller <davem@...hat.com> wrote:
>> >> From: Tom Herbert <therbert@...gle.com>
>> >> Date: Tue, 24 Sep 2013 08:22:55 -0700
>> >>
>> >>> We use this value for steering, and could use it for other uses like
>> >>> connection lookup.
>> >>
>> >> For security reasons we absolutely cannot use it for that purpose,
>> >> please stop claiming this.
>> >>
>> >> Any hash function which an attacker can reproduce is attackable.
>> > 
>> > The Toeplitz function uses a secret key whose length is based on the
>> > input length.  96 bits in IPv4, 320 bits in IPv6.  I don't see how an
>> > attacker can reproduce this if the key is random.  If the problem is
>> > that devices are not being configured with a sufficiently random key
>> > (some actually are using a fixed key :-( ), that's a separate issue
>> > that should be addressed.  It is possible to DoS attack through the
>> > steering mechanism.
>> 
>> All of them are using a fixed, defined, key.
> 
> This is certainly false, as I know sfc randomises the key.  And the
> Microsoft RSS spec appears to require that the key is programmable.

Then I stand corrected.
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